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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 09-30-2012, 04:27 AM   #1
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Default question on battery size and composition to attain c & mah rating

hey gang,today i maidened a 300s extra and the power cut out on the motor resulting in repairs already made to replace the lg/mount and the wing te boltmount that snapped off in the pancake harrier landing. I'll post its power but am more interested in battery assembly and the actual size via manufacture specs on mah/c rates.

power60 eflite.100amp castle ice esc using a sep rx battery,2 very old with many cycles 3cell 4000mah 20c batteries run in series.

i figure the problem may be these old batteries are beginning to sag on cell ability for the motor to draw on the c rating which at 20c is to low. so i now have located replacement batteries.

the important thing was to attain 2 3cell batteries of any reputable manufacturer that would fit the custom battery compartment i made to hold the 2 batteries i have been using. of the many researched batts I've looked at and also taking price into account,i found the zippy 4000mah 40c are smaller than the 3cell 4000mah 20c batteries.

so the question is.....how are batteries made inside so c rating might increase but not the size of the battery. i always thought increase in c results in a much larger battery[not just heavery] these are the 2 batteries in question:

ZIPPY Flightmax 4000mAh 3S1P 40C (USA Warehouse)



Zippy Flightmax batteries deliver full capacity & discharge as well as being the best value batteries in the hobby market today!

Spec.
Capacity: 4000mAh
Voltage: 3S1P / 3 Cell / 11.1v
Discharge: 40C Constant / 50C Burst
Weight: 351g (including wire, plug & case)
Dimensions: 145x50x21mm
Balance Plug: JST-XH
Discharge plug: 4mm








Zippy Flightmax batteries deliver full capacity & discharge as well as being the best value batteries in the hobby market today!

Spec.
Capacity: 4000mAh
Voltage: 3S1P / 3 Cell / 11.1v
Discharge: 20C Constant / 30C Burst
Weight: 306g (including wire, plug & shrink wrap)
Dimensions: 146x51x22mm
Balance Plug: JST-XH
Discharge Plug: Bullet Connector

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 09-30-2012, 09:07 AM   #2
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So you did ground test the plane with a wattmeter to make sure the motor ran reliably at WOT and amps were within spec of all components... right?
if so I'm not sure how you didn't discover the problem before flying.


To answer your question (I'm no expert on battery design by the way).. I'd say that it's down to a few things:
  • Advances in battery technology over time, electrolyte chemistry, construction methods etc.
  • But mainly - Hobbyking massively exaggeration their Zippy battery C rating. I've checked the internal resistance (IR is closely related to C rating) of a brand new 40c zippy and it's about 50% higher than a 30c Gens Ace. I'd say in reality the 40c Zippy is about 20c, at the very best. I suspect that all Zippy's are in reality the same c rating, only the labels are different.
  • The specs quoted on the Hobbyking site have to be taken with a pinch of salt

The root of the problem is that there is no standard telling manufacturers how to arrive as c rating. As it is now they can pretty much make numbers up.

I'm curious about you battery compartment. Usually the batteries are retained on a tray by Velcro and straps. This allows different size batteries to be used but more important it allows the position of the battery to be adjusted for fine tuning of the CG (which is critical for trimming aerobatic models). If you have the batteries locked in a compartment how will you adjust the CG?
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Old 09-30-2012, 01:17 PM   #3
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first...thanks for the reply ,i always do the bench testing with a 30 second wot at the very most to get watt/amp readings and also a very long range check. as a rule I'll consider taxi on the field as the final moment when caution is abandoned for the thrill of flight. what happens then is up in the air. everything appeared to say...extra is ready to go!

i ran wot bench test and am pulling way under the limits of motor and esc. but i haven't done ir testing on batts and frankly don't know how.

your answer to the battery compositions is pretty basic as i also figured on the lack of manufacture lack of a standard for getting c rating. but what i want to know is if it's possible to jam 20 extra c into a smaller battery and is the c rating effected by composition[say added extra lithium] or is this really a bad est of c rating which in my eyes =fraud.

lastly ,your absolutely right about battery box's needing room to move for cg,which is why i build them that way. but i made box's to use these specific size zippies depth/width/thickness. the covers are air scoops for cooling and containments and for the most part I've been using the same batteries for several years,so it's load them in and go.

keep i mind these are my glow to ep conversions where component's are placed forward in the tank area for cg purposes and adding lead rarely is needed.


one more note on zippies,i believe their QC may be in question as i fly a funjet using 4cells and of the 2 batteries i p/u from hk ,sone had an issue with the cut off of motor at wot....this battery eventually puffed after one of it's flight and has been trashed. i think the castle esc sensed the draw on it to be to much.this is the same as whats happening with the extra we're talking about. unfortunately i also use these 3cells in series on the sig hog bipe and haven't had the motor cut on it...if that happens on the sig and it hits terrafirma hard will be a "piss me off" moment as i really like flying the pig. further research is required before i make my next battery purchase. stu

note to fellow flyers:this hobby is very expensive and i really have to add up the $$$$.00 i'v been dumping to keep things going...lol...my wife and kids seem to think food,clothing,house,college is more important.....go figure.[jk]

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Old 09-30-2012, 02:48 PM   #4
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Stuart,

One thing that will help prevent this sudden cut-out when low voltage is detected is setting the Low voltage cut-off to 'Soft'. This means that instead of cutting the motor totally, and potentially causing a crash, the ESC will just throttle back until the battery voltage is above the cut-off level. This gives you chance to land at reduced power.
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Old 09-30-2012, 02:52 PM   #5
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You may find this thread enlightening: The Lipoly Objective Performance Database.

I generally consider HK C ratings to be about 1/2 of the stated value for continuous use. According to the above thread, Gens Ace typically perform closer to their stated values than many other brands.

You may want to consider telemetry. I've used the Quanum system for a couple years and now have Frsky. It's really nice to know what your batteries are actually doing under load, in fight. I set it up beep if any cell drops below 3.5V under load. The Frsky also gives me signal strength and Rx voltage so I know if the UBEC is up to the task.

When batteries no longer perform well under load, I "derate" them and they get used in less demanding planes.

It's never too late to have a happy childhood.
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Old 09-30-2012, 03:05 PM   #6
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Staurt,

To answer your question about how to spot a 'saggy' battery. When you do your ground test make sure the battery is fully charged. Do your usual WOT test and make a note of the peak Watts and Amps.

Now divide the Watts by the Amps and it will give you the loaded battery voltage. Divide the number you get by the number of series cells, this gives you your load voltage per cell.

In my experience:
  • A good battery in good condition operating near it's c limit will hold 3.8v or more per cell
  • 3.8v to 3.6v per cell is showing signs of deterioration (or just poor quality) but depending on level of deterioration is probably still usable.
  • 3.6v per cell or lower and you have some serious voltage sag going on, which is likely to mean you will hit LVC very early in flight, battery near the end of it's life and needs to be used with caution.
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Old 09-30-2012, 04:05 PM   #7
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Agree with all above info.


The 2 packs compared

The length might be explained by a pc board or just simply wiring taking up more room yet shorter cells. It's hard to tell by the pics , but examining the packs may tell.

The height might be explained by foam insulate between cells.

The width is probably accurate.

1 mm I wouldn't consider very significant , yet the weight of the pack is usually what's a dead giveaway to a higher "C" pack. This is true of these 2 packs.

Another explanation may be that the 20C pack just might be a larger actual capacity pack.
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Old 09-30-2012, 08:34 PM   #8
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thanks gang,i think ultimately the 20c's for the power 60 eflite are the issue. i started this hobby mateing packs for different planes in parralel and series and wound up with a lot of 20c packs. from now on it's going to be 30c or higher.

i'm also considering reducing the number of packs i buy and charge at the field. of coarse this means buying the small generator to use on the cellpro pl6 i put together for just this reason. but i'd rather charge up a bunch of packs and just go fly. it's called being to lazy to load the charger box and generator every time i go flying.[i hate the car loading as my hanger is in the basement]

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Old 11-10-2012, 01:55 AM   #9
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Default Dead stick landigs

Might i suggest that everybody practises "Dead Stick" landings. i.e. landing without power and a stationary prop. Hence DEADSTICK. Back in tha day our glow or diesel motors cut when they ran out of fuel and we were forced to land without power. We have the option now to cut power with plenty of height to spare and getting used to handling a Glider/ flying brick. Power can be reduced gradually and powered up again at will. Once used to flying dead at height comme lower and lower making passes at low level and climbing out. then touching and climbing out again. touch & go as it's called in full size flying training. Eventually making full touch downs. Can be a lot of fun and is good practice even make a competition who can make a spot landing. Good luck 1 Have fun. Onetenor
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Old 11-10-2012, 05:55 AM   #10
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Originally Posted by stuart View Post
thanks gang,i think ultimately the 20c's for the power 60 eflite are the issue. i started this hobby mateing packs for different planes in parralel and series and wound up with a lot of 20c packs. from now on it's going to be 30c or higher.

i'm also considering reducing the number of packs i buy and charge at the field. of coarse this means buying the small generator to use on the cellpro pl6 i put together for just this reason. but i'd rather charge up a bunch of packs and just go fly. it's called being to lazy to load the charger box and generator every time i go flying.[i hate the car loading as my hanger is in the basement]
This is one reason why I've standardized on those A123 cells. They are more expensive, about 35% more weight for the same total energy as compared to the LiPos. It's been my experience these A123's work best at about a 20C or less discharge rating. On the other hand, I've got two 12S2P A123 packs that are charged as a 6S4P pack. The charging current is set at 30 Amps with my Cellpro Powerlab 8 charger. So far, I've got battery packs with over 400 flights with zero loss of performance. I'm running those 6S2P and 12S2P cells at about 70 Amps maximum current value.

In another thread in wattflyer, a LiPo mfg is claiming their battery has a 150C rating. That is well over 1000 Amps on the battery specs provided. That with the battery wires size #12. That #12 wire melts at about 350 Amps. IMHO, that 150C rating is not worth the paper its written on.

I don' think these A123'swould don't work out well for the smaller models such as the very popular foamies.

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Old 11-10-2012, 06:01 AM   #11
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Originally Posted by JetPlaneFlyer View Post

But mainly - Hobbyking massively exaggeration their Zippy battery C rating. I've checked the internal resistance (IR is closely related to C rating) of a brand new 40c zippy and it's about 50% higher than a 30c Gens Ace. I'd say in reality the 40c Zippy is about 20c, at the very best. I suspect that all Zippy's are in reality the same c rating, only the labels are different.


The root of the problem is that there is no standard telling manufacturers how to arrive as c rating. As it is now they can pretty much make numbers up.
Good information. What those mfg'rs need to supply to back up their claimed "C" rating is how many charge cycles you will get at their claimed discharge current.

Case in point, one local electric flyer got a total of FIVE flights on each of his three brand new LiPos when they were discharged at their "Rated" continuous C value. The performance dropped off so bad, the batteries were junk. And they were not cheap batteries.

(For the newbies, take a look: http://www.wattflyer.com/forums/showthread.php?t=65869)

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